The invention relates to means for attaching a fore-and-aft sail to a mast of a sailing vessel.
The driving power which the wind imparts to a sailing vessel depends in great measure on the maintenance of proper airflow past the sails. In the customary method of attaching a fore-and-aft sail to a mast, the sail is supported along a vertical track centered on the stern side of the mast. During the exacting maneuver of beating into the wind, however, the sail-mast interaction deriving from the customary attachment method tends to disrupt the airflow over a forward portion of the sail on its leeward side resulting in a loss of driving power.
Disruptions in airflow can arise from the interaction of a sail with the mast or with other sails or from excessive curvature of the sail itself. Experienced sailors strive to mitigate these disruptions in airflow by assiduously optimizing sail camber and trim while underway in response to changes in wind conditions and heading. Although sail chamber is determined largely by the design of the sail itself, a range of adjustment is provided while underway by exerting variable tension on the sail in appropriate directions, and tackle arrangements for this purpose are well known in the prior art. Such efforts for the most part limit the said area over which the disrupted airflow extends and are not particularly directed toward the source of the disruption itself.
It has been recognized heretofore that some increase in sailing efficiency can be achieved when beating into the wind if the mast and forward portion of the sail are disposed relative to one another to form a comparatively smooth surface of aerodynamically efficient shape, thereby reducing the source of airflow disruption directly. To this end, U.S. Pat. No. 3,882,810 employs a mast of triangular cross section specially adapted at its stern side to allow a sail luff to move laterally thereacross and into alignment with one or the other forwardly facing sides of the mast when the vessel is beating to windward. In this configuration a face of the mast and the forward portion of the sail present a continuous surface to the wind. U.S. Pat. No. 4,143,611 employs sailcloth panels equal in length to the sail luff and secured to either side of the mast. The trailing edges of the panels are connected to the luff in such a manner that the luff can traverse from side to side aft of the mast in response to the wind. In this arrangement the mast, a sailcloth panel, and the forward portion of the sail present a smooth, essentially continuous surface to the wind.
Modifications such as these offer smoother, hence less disruptive surfaces to the wind. They typically do so, however, with an accompanying increase in sail camber and deformation of the overall aerodynamic profile of the sail-mast system, leading to less than full harnessing of the wind. Furhermore, they require modifications, sometimes extensive, of the mast, rigging or vessel itself.